Optimizing Reflow Profiles to Control Initial Intermetallic Compound Thickness
Optimizing reflow profiles keeps initial intermetallic compound thickness between 1.5 and 2.5 micrometers, preventing brittle joint fracture.
Cu3Sn Intermetallic Phase
Meaning
Binary alloy layer at the interface between copper and tin represents the result of solid-state diffusion during the soldering of electronic components. The Cu3Sn intermetallic phase is the more copper-rich of the two primary compounds found in solder joints. It appears as a thin layer adjacent to the copper substrate.
Excessive growth of this material can lead to mechanical failure due to its inherent brittleness.
Interfacial Stability
Chemical bonding at the junction creates a durable electrical connection. Growth of the Cu3Sn intermetallic phase continues at a slower rate even at room temperature through solid-state diffusion. While a thin layer is necessary for adhesion, a thick band increases the risk of Kirkendall void formation.
Reliability Risk
Structural defects arise when the atomic flux between layers is unbalanced. The Cu3Sn intermetallic phase consumes the copper pad and can lead to the separation of the solder joint under vibration. Environmental stress testing often focuses on the thickness of this region to predict the long-term durability of the device.
Precise control over peak reflow temperatures prevents the rapid expansion of this brittle alloy.
Material Modification
Barrier layers are often applied to slow down the migration of atoms. Managing the Cu3Sn intermetallic phase requires reducing the duration of the liquid phase during assembly.